Figure 7. Effect of lignin dosage on the oxidation reaction.
Reaction condition: 10 g (12 mL) microemulsion (WW:WO :WP = 15.7 :9.2 :75.1,wt. %), 0.1 mmol CuSO4, 25.0 mmol L-1 H2SO4, 1 MPa O2, 433 K, 4 h.
The effect of initial lignin dosage on its own oxidation in the microemulsion reactor (point c in Figure 3) was studied to investigate the capacity of this novel reactor under the optimized reaction conditions. It is clearly seen in Figure 7, that the total mass of phenolic monomers grows linearly with the increasing mass of lignin. When the lignin dosage changes from 0.1 to 0.5 g, the total mass of phenolic monomers grows from 12.7 to 57.7 mg, while the loss of total yield of phenolic monomers is no more than 10% (127.1 to 115.1 mg g-1). This demonstrates that this SFME reactor is efficient with a remarkable capacity up to 40.8 g L-1 at 0.5 g lignin dosage, even by the comparison to the outstanding works about the oxidation of lignin in ionic liquid or aqueous system (12.5 and 10 g L-1respectively).9, 46 Moreover, by consideration of lignin solubility in this system (79.1 g L-1), the capacity of the microemulsion reactor can be much higher for lignin oxidation, since the maximum concentration (40.8 g L-1) is just near to half of its solubility in this study.